This invention relates to levels for determining how much the heights of two spaced points of a surface or of respective related surfaces must be changed to position the points precisely on a horizontal line.
The prevalent levels or spirit levels used in carpentry have bubble vials that are fixed in respective bars or beams. The vials are adjusted with respect to the main bodies of the levels only initially or occasionally for determining either level surfaces or inclined surfaces at fixed angles. Means are not provided for determining accurately how much the structural members must be moved or tilted to obtain the desired position.
Levels that are more precise than those used in carpentry are required for such uses as the leveling of machine tools and the aligning of two adjacent machines that have interconnecting drive shafts. The bubble vials in precision levels are made to be sensitive enough to show much smaller changes of inclination than the changes required to be shown by the vials of usual levels. For calibration and for measuring slightly different inclinations, the vials are mounted on respective pivoted members to permit accurately controlled variations in the inclinations of the vials with respect to the respective main bodies of the levels. Levels permitting variations by screw adjustments are shown in U.S. Pat. No. 3,307,269 issued to E. S. Karstens on Mar. 7, 1967.
In addition to having adjustable vials, precision levels have means for measuring the difference in heights of two points or how far the points are off level. For example, in a level according to the Karstens patent mentioned above, each end of the main body of the level is supported above a point by a bracket assembly and has a screw for setting accurately the height of the end of the main body above one of two points that are being compared in height. While the level is in a first position to be supported over the two points, the inclination of the vial is adjusted until its bubble is in a reference position. The level is then turned end for end to support the level over the two points, and the screw at one end or the screws at both ends for adjusting the height of the respective ends of the main body are adjusted until the bubble in the vial is again at the reference position. Micrometer means connected between the body of the level and the supporting means where the height is adjusted provides a reading in the change in height between the end of the body of the level and the point supporting that end. Since this reading is twice the difference in the heights of the two points, the micrometer means at one end of the level is then adjusted for a change of reading of one-half of the change in reading that was required to position the bubble at the reference position immediately after the level had been reversed. If the two points are on separate structures, the height of one or both of the structures is changed until the change in height between the two is equal to this one-half reading displayed on the micrometer means. If the procedure has been performed accurately, the bubble is returned to its reference position by the adjustment in height of the structures. The points should then be at the same level, and the accuracy of the leveling can be determined by again reversing the level to its original position and checking to see if the bubble is still at its reference position.